We have produced HAV "epitope libraries" in the expression vector lambda gt 11. A fragment of HAV cDNA representing the entire capsid coding region was isolated. Random fragments of this DNA were produced by limited DNase digestion and these fragments were cloned into lambda gt 11. These libraries were screened by neutralizing monoclonal antibodies, but specific clones were not identified. However, anti-peptide antibodies representing regions from all four capsid proteins readily identified clones. These results suggest that the epitopes recognized by these antibodies are discontinuous or conformational and a different approach will be required to identify them. A larger battery of monoclonal antibodies is now being used to screen the libraries.